Process for refining gasoline



21, 1956 A. GISLON EI'AL 2,759,874

PROCESS FOR REFINING GASOLINE Filed March 15, 1949 2 Sheets-Sheet l F/Ig. 7.

l NVENTOR And/ e 0584010 J'ose fa aw were I fay Q 4 ATTORN Y 1956 A. GISLON EIAL PROCESS FOR REFINING GASOLINE 2 Sheeis-Sheet 2 Filed March 15, 1949 INVENTOR c742??? Gzlsron ?se;0 QMQUBP? ATTO EY United States Patent PROCESS FOR REFINING GASOLINE Andr Gislon, Paris, and Joseph Quiquerez, Saint-Cloud, France assignors to Societe Anonyme dite: Compagnie grancarse de Raffinage, Paris, France, a corporation of rance Application March 15, 1949, Serial No. 81,584 Claims priority, application France April 9, 1948 9 Claims. (Cl. 196-29) The treatment of gasoline with sodium plumbite for eliminating the mercaptans involves, according to the usual method of procedure, adding sulphur to the gasoline-plumbite mixture, the quantity of sulphur added being accurately closed to produce the oxidation of the lead mercaptide into organic disulphide and lead sulphide. It is known how important this dosing is in this technique, since on the one band a slightly insufiicient quantity of sulphur leaves lead mercaptide in the gasoline and it is furthermore found that the precipitation of the lead sulphide is extremely deficient, thereby abnormally lengthening the operation, and on the other hand if an excessive quantity of sulphur is added, a corrosive gasoline is obtained. In this same technique, after adding sulphur and decanting the gasoline, the lead sulphide precipitated in the aqueous alkaline plumbite solution is oxidized by the air into lead oxide, whereby the plumbite solution is regenerated. This oxidation produces alkali thiosulphate and it is known that the increase of the concentration of same in the solution makes it necessary, when it exceeds about 20%, to eliminate it with all the lead it still contains.

Attempts have already been made to elimiate the addition of sulphur and in a number of processes the sulphur is replaced by air. It has been proposed, in particular, to treat gasoline with sodium plumbite, separate the two phases and treat the hydrocarbon layer containing the lead mercaptides with air in the presence of an aqueous solution of fresh caustic soda and lead sulphide that acts as a catalyst. It should be noted that in this technique, the aqueous layer formed by an alkaline plumbite solution that also contains lead or sodium mercaptides has to be regenerated in order to obtain an economical working. This regeneration by oxidation can only be readily effected with sulphur, since at the temperatures at which the oxidation has to be effected, a hydrolysis takes place which releases the mercaptans which are not so readily oxidizable by air as mercaptides. The treatment of the layer formed by the gasoline, carried out in the presence of soda and lead sulphide, leads to the formation of plumbite, the lead finally coming from the lead mercaptide which is soluble in gasoline, and from the lead sulphide which is used as a catalyst. However, the concentration of the plumbite solution formed is diflicult to control and it should furthermore be noted that the presence of caustic soda in this operation is very unfavorable for the oxidation of the mercaptides.

The present invention has for its object a process for sweetening gasoline and for continuously regenerating the plumbite solutions involved.

Said process-which is based on a suitable combination of alkaline treatments, plumbite treatment and oxidation with air of the mercaptides under rational conditions-is characterised by the following sequence of operations:

The gasoline to be treated is first of all washed with a caustic soda solution so as to eliminate all the mercaptans which are soluble in the aqueous phase.

A treatment is then effected with a solution of sodium plumbite. We have observed that the lead mercaptides which are thus formed are completely soluble in the hydrocarbon phase, so that there'is no need to efiect an oxidation of the mercaptans in the plumbite alkaline phase.

After decantation, separation is therefore effected, on the one hand of an aqueous layer which is impoverished in lead by the quantity which is combined with the mercaptans and enriched in sodium by the corresponding quantity by displacement of the lead previously combined in the form of plumbite, and on the other hand of a gasoline layer containing all the mercaptans in the form of lead mercaptides. This hydrocarbon phase is subjected to the action of air, by any known means, at a temperature of to 150 C. and a sufficient pressure to keep said phase in a liquid state. It should be noted that this treatment is effected without any alkaline aqueous phase. Under these conditions, the lead mercaptides are oxidized into disulphides which are soluble in gasoline and into lead oxide which precipitates. The gasoline is separated and the precipitate is re-treated in the plumbite solution which was used for the treatment. It quickly dissolves therein and thus re-forms the original plumbite solution; this solution is used in the treatment of further quantities of gasoline.

The process can be carried out in the apparatus shown by way of example in Fig. l of the accompanying drawmg.

The gasoline is first washed with caustic soda, and then enters the apparatus through the pipe 1. It is treated in a static mixer 2 with a plumbite solution (120 grams of caustic soda-{-30 to 40 grams of PbO per litre) stored in the tank 3. In the decanter 4, the spent plumbite solution is separated in the lower layer, and the gasoline containing the lead mercaptides is separated in the upper layer. This gasoline is delivered by a pump P, with introduction of air at 5, into a mixer 6 in which it is heated to about C. The gasoline is then allowed to decant in 7. The lead oxide separates out in the form of a sludge which deposits at the bottom of the decanter. The air is exhausted at the top at 8 and is suitably separated, by any known means, from the gasoline carried away. The gasoline is removed through the lateral pipe 9. The PbO sludge which is removed at 10 is mixed, either after merely decanting, or after centrifuging, in a mixer 11 with the spent plumbite removed from the decanter 4. A decanter 12 enables the gasoline carried away with the PbO sludge to be separated; this gasoline is removed at 13; the regenerated plumbite removedat 14 is returned to the tank 3. The sweet gasoline flows out of the apparatus at 15.

This gasoline contains, in the form of disulphide, all the sulphur that was originally present in the form of merchaptans (after the caustic soda treatment, of course). Now, it is known that disulphides are undesirable inasmuch as they substantially lower the susceptibility of the gasoline to tetraethyl lead. It is therefore necessary to eifect a redistillation of the gasoline.

An advantageous modification of the process according to the invention comprises effecting this distillation after the plumbite treatment and before the oxidation of the mercaptans into disulphides; in this manner, the lead mercaptides are concentrated in the heavy fractions of the gasoline, and only said heavy fractions are subjected to the oxidizing treatment with air. This modification has a treble technical advantage:

On the one hand, the oxidation of the mercaptides is effected on a small quantity of the orignal gasoline, thereby decreasing the volume of the oxidation apparatus and of the apparatus for separating the lead oxide.

On the other hand, owing to the high boiling point of said heavy fractions of the gasoline, the treatment with air can be effected at atmospheric pressure.

Finally, since the distilled gasoline no longer contains either mercaptans or corresponding disulphides, it has a higher octane number and a higher susceptibility to tetraethyl lead.

Furthermore, this modification has the following economical advantages: whereas in the redistillation of the gaso'lines enriched in disulphides which are obtained by means of the usual plumbite treatments, it is necessary to effect a fractionated distillation owing to the volatility of the disulphides, in the process according to the present invention, on the contrary, owing to the non-volatility of the lead mercaptides, it is only necessary to effect a concentration, which is .an operation that can be effected in a distillation without reflux; the concentration can be carried further as the temperature of the residue is kept lower to prevent a disintegration of the lead mercaptide which would release volatile mercaptans; in general, it is only necessary to complete the concentration in a suitable vacuum in order to limit the temperature of the residue to about 150180 C.

The apparatus shown by way of example in Fig. 2, which is not limitative, enables this modification of the invention to be carried out.

The gasoline is washed beforehand with caustic soda and then enters the apparatus through the pipe 16. In the mixer 17 it is treated with the plumbite solution sucked from the tank 18 by the injector 19, and then flows into the decanter 20. in said decanter 20, the spent plumbite solution is separated through the pipe 21, and the gasoline containing the lead mercaptides is separated through the pipe 22. Said gasoline is concentrated without air, for example in an atmosphere of inert gas, in the evaporators 23 and 24 in such a manner as to leave a residue of about 3 to with respect to the original gasoline. The last evaporator, which operates in a suitable vacuum exerted at 25, so as to keep the temperature of the residue below 150 C., may if desired be heated by the vapors issuing from the first evaporator.

Under these conditions, about 95 to 97% of the original gasoline is extracted from the condenser 26 through the pipe 27, without any mercaptan and other disulphides except those that existed beforehand in said gasoline.

The residue enriched in lead mercaptide is removed through the pipe 28 and treated with air supplied through 29, in the mixer 30, at atmospheric pressure at 150 C. The decanter 31 enables the excess of air to be exhausted at 32, the heavy gasoline to be removed at 33 and the lead oxide sludge to be withdrawn at 34. Said sludge, I

which may optionally be centrifuged, is redissolved in th mixer 35 heated to about 50 C. in the spent plumbite solution removed from the decanter through the pipe 21. A last decanter 36 enables the last quantities of heavy gasoline carried along with the lead oxide, to be separated from the regenerated plumbite solution which is returned to the storage tank 18 through the pipe 37.

If it is desired to remove all the original gasoline from the concentrator, a heavy hydrocarbon, for example a kerosene fraction, which acts as a vehicle for the lead mercaptide, may be added in the last element 24.

What we claim is:

l. A process for eliminating mercaptans from liquid petroleum products which comprises treating said petroleum products with caustic soda solution to thereby remove alkali soluble mercaptans, separating said treated petroleum products from the caustic soda solution, thereafter treating said petroleum products with a solution of sodium plumbite to form hydrocarbon-soluble lead mercaptides, separating the hydrocarbon phase from the aqueous phase, treating said separated hydrocarbon phase with air at an elevated temperature whereby to precipitate lead oxide and to form hydrocarbon-soluble disulfides,

2. A process according to claim 1 wherein precipitated lead oxide is separated from the hydrocarbon phase and is then dissolved in the partially spent sodium plumbite solution thereby regenerating said solution.

3. A process according to claim 2 wherein the treatment of the hydrocarbon phase with air is carried out at a temperature between about and C.

4. A continuous process for eliminating mercaptans from liquid petroleum hydrocarbons which comprises first washing said hydrocarbons with caustic soda solution to dissolve alkali-soluble mercaptans in the solution, separating the washed hydrocarbons from the alkali solution, adding a solution of sodium plumbite to the washed hydrocarbons to thereby form hydrocarbon-soluble lead mercaptides, separating the partially spent sodium plumbite solution from the treated hydrocarbons, and aerating said treated hydrocarbons with air at a temperature sufficient to transform said lead mercaptides into hydrocarbonsoluble disulfides and to precipitate lead oxide from the hydrocarbons.

5. A process according to claim 4 with the addition of separating the precipitated lead oxide from the aerated hydrocarbons, and dissolving said precipitated lead oxide in the partially spent plumbite solution thereby regenerating the said plumbite solution.

6. A process for eliminating mercaptans from liquid hydrocarbons which comprises washing said hydrocarbons with a caustic soda solution to remove alkali-soluble mercaptans, then separating said hydrocarbons from said alkali solution, thereafter treating the washed hydrocarbons with a solution of sodium plumbite in order to form hydrocarbon-soluble lead mercaptides, separating said treated hydrocarbons from said plumbite solution, then distilling said hydrocarbons to concentrate said hydrocarbon-soluble lead mercaptides in the heavy hydrocarbon distillation residue, thereafter separately aerating said distillation residue with air at an elevated temperature to transform said lead mercaptides into hydrocarbon-soluble disulfides and to precipitate lead oxide, separating precipitated lead oxide from said aerated distillation residue and finally dissolving said separated lead oxide in the partially spent plumbite solution to regenerate it.

7. A process according to claim 6 wherein said distillation is conducted in a plurality of stages at least one of which is maintained at sub-atmospheric pressure.

8. A process according to claim 6 with the additional step of adding a small amount of a heavy hydrocarbon liquid to, the hydrocarbon to be treated to thereby act as a vehicle for the hydrocarbon-soluble lead mercaptides.

9. A process according to claim 6 with the additional step of adding a small amount of a heavy hydrocarbon for vehicling the lead mercaptides, after the hydrocarbons have been subjected to the alkali wash.

References Cited in the file of this patent UNITED STATES PATENTS 1,789,335 Fischer et al. Jan. 20, 1931 1,968,089 Morrell July 31, 1934 2,042,055 Hoover May 26, 1936 2,334,549 Gilbert Nov. 16, 1943 2,336,109 Lowry et al Dec. 7, 1943 2,340,157 Thacker Jan. 25, 1944 2,347,515 Shmidl Apr. 25, 1944 2,356,704 Shmidl et al. Aug. 22, 1944 2,417,280 Viles Mar. 11, 1947 2,478,603 Stratton Aug. 9, 1949 OTHER REFERENCES Kalichevsky et al.: Chemical Refining of Petroleum, 2nd ed., pages and 187 (1942). 

1. A PROCESS FOR ELIMINATING MERCAPTANS FROM LIQUID PETROLEUM PRODUCTS WHICH COMPRISES TREATING SAID PETROLEUM PRODUCTS WITH CAUSTIC SODA SOLUTION TO THEREBY REMOVE ALKALI SOLUBLE MERCAPTANS, SEPARATING SAID TREATED PETROLEUM PRODUCTS FROM THE CAUSTIC SODA SOLUTION, THEREAFTER TREATING SAID PETROLEUM PRODUCTS WITH A SOLUTION OF SODIUM PLUMBITE TO FORM HYDROCARBON-SOLUBLE LEAD MERCAPTIDES, SEPARATING THE HYDROCARBON PHASE FROM THE AQUEOUS PHASE, TREATING SAID SEPARATED HYDROCARBON PHASE WITH AIR AT AN ELEVATED TEMPERATURE WHEREBY TO PRECIPITATE LEAD OXIDE AND TO FORM HYDROCARBON-SOLUBLE DISULFIDES. 